Liquid radiation curable resins for additive fabrication comprising a triaryl sulfonium borate cationic photoinitiator

ABSTRACT

Liquid radiation curable resins for additive fabrication comprising an R-substituted aromatic thioetber triaryl sulfonmm tetrakis(pentafluorophenyl)borate cationic photoinitiator is disclosed. A process for using the liquid radiation curable resins for additive fabrication and three-dimensional articles made from the liquid radiation curable resins for additive fabrication are also disclosed.

FIELD OF THE INVENTION

The present invention relates to liquid radiation curable resins foradditive fabrication processes.

BACKGROUND OF THE INVENTION

Additive fabrication processes for producing three dimensional objectsare known in the field. Additive fabrication processes utilizecomputer-aided design (CAD) data of an object to build three-dimensionalparts. These three-dimensional parts may be formed from liquid resins,powders, or other materials.

A non-limiting example of an additive fabrication process isstereolithography (SL). Stereolithography is a well-known process forrapidly producing models, prototypes, patterns, and production parts incertain applications. SL uses CAD data of an object wherein the data istransformed into thin cross-sections of a three-dimensional object. Thedata is loaded into a computer which controls a laser beam that tracesthe pattern of a cross section through a liquid radiation curable resincomposition contained in a vat, solidifying a thin layer of the resincorresponding to the cross section. The solidified layer is recoatedwith resin and the laser beam traces another cross section to hardenanother layer of resin on top of the previous layer. The process isrepeated layer by layer until the three-dimensional object is completed.When initially formed, the three-dimensional object is, in general, notfully cured and therefore may be subjected to post-curing, if required.An example of an SL process is described in U.S. Pat. No. 4,575,330.

There are several types of lasers used in stereolithography, rangingfrom 193 nm to 355 nm in wavelength. The use of bulky and expensive gaslasers to cure liquid radiation curable resins is well known. Thedelivery of laser energy in a stereolithography system can be ContinuousWave (CW) or Q-switched pulses. CW lasers provide continuous laserenergy and can be used in a high speed scanning process. However, theiroutput power is limited which reduces the amount of curing that occursduring object creation. As a result the finished object will needadditional post process curing. In addition, excess heat could begenerated at the point of irradiation which may be detrimental to theresin. Further, the use of a laser requires scanning point by point onthe resin which can be time-consuming.

Other methods of additive fabrication utilize lamps or light emittingdiodes (LEDs). LEDs are semiconductor devices which utilize thephenomenon of electroluminescence to generate light. LEDs consist of asemiconducting material doped with impurities to create a p-n junctioncapable of emitting light as positive holes join with negative electronswhen voltage is applied. The wavelength of emitted light is determinedby the materials used in the active region of the semiconductor. Typicalmaterials used in semiconductors of LEDs include, for example, elementsfrom Groups 13 (III) and 15 (V) of the periodic table. Thesesemiconductors are referred to as III-V semiconductors and include, forexample, GaAs, GaP, GaAsP, AlGaAs, InGaAsP, AlGaInP, and InGaNsemiconductors. Other examples of semiconductors used in LEDs includecompounds from Group 14 (IV-IV semiconductor) and Group 12-16 (II-VI).The choice of materials is based on multiple factors including desiredwavelength of emission, performance parameters, and cost.

Early LEDs used gallium arsenide (GaAs) to emit infrared (IR) radiationand low intensity red light. Advances in materials science have led tothe development of LEDs capable of emitting light with higher intensityand shorter wavelengths, including other colors of visible light and UVlight. It is possible to create LEDs that emit light across a widewavelength spectrum, for example, from a low of about 100 nm to a highof about 900 nm. Typically, LED UV light sources currently emit light atwavelengths between 300 and 475 nm, with 365 nm, 390 nm, and 395 nmbeing common peak spectral outputs. See textbook, “Light-EmittingDiodes” by E. Fred Schubert, 2^(nd) Edition, © E. Fred Schubert 2006,published by Cambridge University Press.

Several manufacturers offer LED lamps for commercial curingapplications. For example, Phoseon Technology, Summit UV, Honle UVAmerica, Inc., IST Metz GmbH, Jenton International Ltd., Lumos SolutionsLtd., Solid UV Inc., Seoul Optodevice Co., Ltd., SpectronicsCorporation, Luminus Devices Inc., and Clearstone Technologies, are someof the manufacturers offering LED lamps for curing ink-jet printingcompositions, PVC floor coating compositions, metal coatingcompositions, plastic coating composition, and adhesive compositions.

LED curing devices are used in dental work. An example of such a deviceis the ELIPAR™ FreeLight 2 LED curing light from 3M ESPE. This deviceemits light in the visible region with a peak irradiance at 460 nm. LEDequipment is also being tested for use in the ink-jet printing,including, for example, by IST Metz. Although LED lamps are available,liquid radiation curable resins suitable for additive fabrication andcurable by the use of LED light are not well known commercially.

Although LED lamps are available, photocurable compositions suitable foradditive fabrication and curable by the use of LED light are not wellknown commercially. Laser curable resins are more common. For example,U.S. Pat. No. 7,211,368 reportedly discloses a liquid stereolithographyresin comprising a first urethane acrylate oligomer, a first acrylatemonomer, a polymerization modifier, a second urethane acrylate oligomerdifferent from the first urethane acrylate oligomer, and a stabilizer.The first urethane acrylate oligomer is an aliphatic polyester urethanediacrylate oligomer, the first acrylate monomer is ethoxylated (3)trimethylolpropane acrylate, and the polymerization modifier is selectedfrom the group consisting of isobornyl acrylate, ethoxylated (5)pentaerythritol tetraacrylate, an aliphatic urethane acrylate,tris-(2-hydroxyethyl)isocyanurate triacrylate, and mixtures thereof. Theresin includes 5-35 weight % of an aliphatic polyester urethanediacrylate oligomer and 0.5-25 weight % ethoxylated (3)trimethylolpropane acrylate, wherein the resin includes 15-45 weight %ethoxylated (5) pentaerythritol tetraacrylate. However, the '368 patentindicates that a laser is used to cure the resin. Further, the '368patent fails to disclose the use of an acid generating photoinitiator,such as a cationic photoinitiator.

More recently, some attention has been given to the use of LEDs inadditive fabrication processes. U.S. Pat. No. 6,927,018 and U.S. PatentApplication Publication No. 2005/0227186 purportedly provide a method,article of manufacture and system for fabricating an article usingphoto-activatable building material. The method according to the '018patent and the '186 publication includes the steps of applying a layerof the photo-activatable building material to a preselected surface,scanning the layer using a plurality of light-emitting centers tophoto-activate the layer of photo-activatable building material inaccordance with a predetermined photo-initiation process to obtainpolymerization of the building material. Scanning is accomplished at apredetermined distance using a predetermined light intensity, andrepeating the steps of applying the layer. Each layer is applied to animmediately previous layer, and the layer is scanned with the pluralityof light-emitting centers to polymerize the building material until thearticle is fabricated. While the '018 patent and the '186 publicationmention UV LEDs and laser diodes as suitable light-emitting centers,they fail to disclose detailed information on photo-activatable buildingmaterial suitable for LED cure.

U.S. Pat. No. 7,270,528 purportedly discloses a flash curing system forsolid freeform fabrication which generates a plurality of radiationemitting pulses that forms a planar flash. The planar flash initiatescuring of a curable material dispensed by a solid freeform fabricationapparatus. The '528 patent, while mentioning UV light-emitting diodes(LED) lamps in the specification, sets forth examples where a flash lampis used to cure the resin composition. The resin composition illustratedin the '528 patent does contain a cationically curable monomer or acationic photoinitiator.

U.S. Patent Application Publication No. 2008/0231731 or 2008/0169589 orEuropean Patent Application No. EP 1950032 purportedly discloses a solidimaging apparatus that includes a replaceable cartridge containing asource of build material and an extendable and retractable flexibletransport film for transporting the build material layer-by-layer fromthe cartridge to the surface of a build in an image plane. If desired,the apparatus can produce a fully reacted build. A high intensity UVsource is said to cure the build between layers. The above publicationsstate that the solid imaging radiation that is used to cure the buildmaterial can be “any actinic radiation which causes a photocurableliquid to react to produce a solid, whether a visible or UV source orother source,”

International Patent Publication No. WO 2008/118263 is directed to asystem for building a three-dimensional object based on build datarepresenting the three-dimensional object, wherein the system includesan extrusion head that deposits a radiation-curable material inconsecutive layers at a high deposition rate. The radiation-curablematerial of each of the consecutive layers is cooled to aself-supporting state. The system is said to include a radiation sourcethat selectively exposes portions of the consecutive layers to radiationat a high resolution in accordance with the build data. It is statedthat the exposure head includes a linear array of high resolution, UVlight-emitting diodes (LEDs). P71-1464 CUREBAR™ and P150-3072 PRINTHEAD™are described as examples of suitable UV-radiation sources for theexposure head. The '263 publication fails to describe exemplaryphotocurable formulations suitable for curing by LED light in anadditive fabrication process.

International Patent Publication No. WO 2005/103121, entitled “Methodfor photocuring of Resin Compositions”, assigned to DSM IP Assets B.V.,describes and claims Methods for Light Emitting Diode (LED) curing of acurable resin composition containing a photoinitiating system,characterized in that the highest wavelength at which absorption maximumof the photoinitiating system occurs (λ_(Max PIS)) is at least 20 nmbelow, and at most 100 nm below, the wavelength at which the emissionmaximum of the LED occurs (λ_(LED)). The invention in this PCT patentapplication relates to the use of LED curing in structural applications,in particular in applications for the lining or relining of objects, andto objects containing a cured resin composition obtained by LED curing.This invention provides a simple, environmentally safe and readilycontrollable method for (re)lining pipes, tanks and vessels, especiallyfor such pipes and equipment having a large diameter, in particular morethan 15 cm. The specification does not describe LED radiation curablephotocurable resins.

U.S. Patent Application Publication No. 2007/0205528 reportedlydiscloses an optical molding process wherein the radiation source usedis a non-coherent source of radiation. The '528 publication indicatesthat the photocurable compositions are formulated so as to enable theproduction of three-dimensional articles having better performance whenirradiated with conventional (non-coherent) UV rather than with LaserUV, and states that the photocurable compositions disclosed are moreappropriate for UV non-coherent irradiation than for Laser UV. While the'528 publication mentions that “the exposure system uses irradiationfrom non-coherent light sources, e.g., a xenon fusion lamp, or lightemitting diode bars,” the exemplified exposure was reportedly carriedout according to the method of WO 00/21735, which is said to describe anapparatus and a method wherein the photosensitive material is exposed toa light source illuminating a cross-section of a material by at leasttwo modulator arrangements of individually controllable lightmodulators.

U.S. Patent Application Publication No. 2009/0267269A or WO 2009/132245reportedly discloses a continuous-wave (CW) ultraviolet (UV) curingsystem for solid freeform fabrication (SFF), wherein the curing systemis configured to provide an exposure of UV radiation for one or morelayers of UV-curable material. It is reported that one or more UVexposures may initiate curing of a curable material in the layerdispensed by a solid freeform fabrication apparatus. According to the'269 or '245 publication, one approach to provide the single or multipleUV exposures is the use of one or more UV LEDs, which generate UVradiation without generating any substantial amounts of infrared (IR)radiation at the same time.

The foregoing shows that there is an unmet need to provide photocurableresin compositions for additive fabrication which are capable of curingby irradiation by LED light.

Regardless of which type of light source is used in an additivefabrication process, it is well known in the field of liquid radiationcurable resins that hybrid liquid radiation curable resins produce curedthree-dimensional articles with the most desirable combination ofmechanical properties. A hybrid liquid radiation curable resin is aliquid radiation curable resin that comprises both free radical andcationic polymerizable components and photoinitiators. It is also wellknown that the cationically polymerizable components of a liquidradiation curable resin primarily contribute to the desirablecombination of mechanical properties in a cured three-dimensionalarticle, however, the cationically polymerizable components of a liquidradiation curable resin polymerize at a much slower rate than thefree-radically polymerizable components. Consequently, the mechanicalproperties of the cured three-dimensional article develop over timeafter the initial cure of the hybrid liquid radiation curable resin.Liquid radiation curable resins for additive fabrication that containcationically polymerizable components but no free-radical polymerizablecomponents are known, however, such resins are generally considered tobe too slow for use as rapid prototyping materials. Therefore, it isdesired to increase the speed of the cationic cure in a liquid radiationcurable resin for additive fabrication to enable the resin to attain themost desirable combination of physical properties as quickly aspossible.

Since the cationic polymerizable components generally cure at a muchslower rate than free-radical polymerizable components, it is highlydesirable to speed the rate of cationic cure. Moreover, it is desirableto attain a resin with a fast photospeed that uses less photoinitiatorso that the amounts of the components that positively contribute to themechanical properties of a three-dimensional article formed from theliquid radiation curable resin can occupy a greater percentage of theliquid radiation curable resin. Furthermore, cationic photoinitiatorsthat provide excellent photospeed at a variety of wavelengths commonlyused in additive fabrication techniques are highly desirable.

Many cationic photoinitiators useful in additive fabrication also havepoor thermal-stability. Thermal-stability is the ability of a liquidradiation curable resin to maintain its viscosity after exposure totemperature over time or during storage. Cationic photoinitiators areresponsive to both light and temperature. At elevated temperatures, orat ambient temperature for a long time period, the cationicphotoinitiators will be slowly activated and initiate a small amount ofpolymerization in the liquid radiation curable resin. Over time, thissmall amount of polymerization will create an undesirable increase inthe viscosity of the liquid radiation curable resin for additivefabrication.

Hybrid liquid radiation curable resins that contain high amounts ofinorganic filler, so-called filled compositions, are highly desirablebecause of the combination of strength and stiffness of the fully curedobjects. Silica filler has been the most preferred inorganic filler forliquid radiation curable resins for additive fabrication for a number ofyears. Please see for example, US published applications 2006/0100301,assigned to DSM, and 2005/0040562, assigned to 3D Systems. Silicaparticles are predominately comprised of SiO₂. Examples of commercialembodiments of filled liquid radiation curable resins wherein silicananoparticles are present are NanoTool™ and NanoForm™ 15100 Series byDSM Somos® and Accura® BlueStone™ by 3D Systems, Inc.

A high amount of inorganic filler is highly desirable in a liquidradiation curable resin due to its impact on the strength and stiffnessof the three-dimensional object produced therefrom. However, highlyfilled compositions represent several challenges to the formulator ofliquid radiation curable resins for additive fabrication. As the amountof filler increases, the viscosity of the liquid radiation curable resinalso usually increases. A high viscosity liquid radiation curable resinis not desirable in some additive fabrication processes, for instance,stereolithography.

Furthermore, certain highly filled compositions are usually not asphoto-stable as non-filled liquid radiation curable resins for additivefabrication. Photo-stability is the ability of a liquid radiationcurable resin to maintain its viscosity after exposure to ambient lightand undesirable light scattering in additive fabrication machines.Because liquid radiation curable resins for additive fabrication includeone or more photoinitiators that are responsive to ambient lightundesirable light scattering that occurs in additive fabricationprocesses, partial polymerization occurs in the liquid radiation curableresin after it is exposed to light. This small amount of polymerization,over time, causes the viscosity of the liquid radiation curable resin toincrease gradually. Achieving good photo-stability is particularlychallenging in highly filled liquid radiation curable resins because ofadditional light scattering effects caused by the filler.

The most used cationic photoinitiators for current liquid radiationcurable resins for additive fabrication are based upon sulfonium oriodonium cations in combination with either fluorophosphates orfluoroantimonate anions. Antimonate salts are often preferred because oftheir fast rate of cure. However, in some municipalities, objectsfabricated from antimonate based compositions must be disposed of as ahazardous waste or hazardous constituent waste.

Furthermore, it is often desirable to have low antimony or antimony-freeradiation curable compositions due to the adverse effect of antimonatesalts on the desired applications of the three-dimensional article. Forexample, antimonate salts can have an undesirable effect in investmentcasting applications. Iodonium-borate photoinitiators are available, butsuffer from the need to be sensitized at the wavelengths useful forstereolithography and have low thermal-stability. Sulfonium phosphatephotoinitiators are available, but suffer from a poor rate of curing.

It would be desirable to have a cationic photoinitiator for additivefabrication that has fast photospeed, good photo-stability in filledcompositions, good thermal-stability, and is antimony-free.

BRIEF SUMMARY OF THE INVENTION

The first aspect of the instant claimed invention is a liquid radiationcurable resin for additive fabrication comprising an R-substitutedaromatic thioether triaryl sulfonium tetrakis(pentafluorophenyl)boratecationic photoinitiator with a tetrakis(pentafluorophenyl)borate anionand a cation of the following formula (I):

wherein Y1, Y2, and Y3 are the same or different and where Y1, Y2, or Y3are R-substituted aromatic thioether with R being an acetyl or halogengroup.

The second aspect of the instant claimed invention is a process offorming a three-dimensional object comprising the steps of forming andselectively curing a layer of a liquid radiation curable resin foradditive fabrication of the first aspect of the instant claimedinvention and repeating the steps of forming and selectively curing alayer of a liquid radiation curable resin for additive fabrication ofthe first aspect of the instant claimed invention a plurality of timesto obtain a three-dimensional object.

The third aspect of the instant claimed invention is a three-dimensionalobject formed from the liquid radiation curable resin for additivefabrication of the first aspect of the instant claimed invention.

The fourth aspect of the instant claimed invention is a liquid radiationcurable resin for additive fabrication comprising 5 wt % to about 90 wt%, preferably from 10 wt % to 75 wt %, more preferably from 30 to 75 wt% of inorganic filler, said inorganic filler preferably comprisinggreater than 80 wt %, preferably greater than 90 wt %, more preferablygreater than 95 wt % of silica, that has a Dp of from about 4.5 mils toabout 7.0 mils wherein the liquid radiation curable resin for additivefabrication, when placed on a shaker table set at 240 rpm and exposed totwo 15 watt plant and aquarium lamps hung 8 inches above the surface ofthe liquid radiation curable resin for additive fabrication, has a geltime of greater than 200 hours, preferably greater than 250 hours.

The fifth aspect of the instant claimed invention is the use of anR-substituted aromatic thioether triaryl sulfoniumtetrakis(pentafluorophenyl)borate cationic photoinitiator with atetrakis(pentafluorophenyl)borate anion and a cation of the followingformula (I):

wherein Y1, Y2, and Y3 are the same or different and where Y1, Y2, or Y3are R-substituted aromatic thioether with R being an acetyl or halogengroup, on metal and metal alloys.

DETAILED DESCRIPTION OF THE INVENTION

U.S. Provisional application 61/287,620 is hereby incorporated byreference in its entirety.

The first aspect of the instant claimed invention is a liquid radiationcurable resin for additive fabrication comprising an R-substitutedaromatic thioether triaryl sulfonium tetrakis(pentafluorophenyl)boratecationic photoinitiator with a tetrakis(pentafluorophenyl)borate anionand a cation of the following formula (I):

wherein Y1, Y2, and Y3 are the same or different and wherein Y1, Y2, orY3 are R-substituted aromatic thioether with R being an acetyl orhalogen group.

R-Substituted Aromatic Thioether Triaryl SulfoniumTetrakis(Pentafluorophenyl)Borate Cationic Photoinitiator

In accordance with an embodiment, the liquid radiation curable resin foradditive fabrication comprises an R-substituted aromatic thioethertriaryl sulfonium tetrakis(pentafluorophenyl)borate cationicphotoinitiator. The cationic photoinitiator generates photoacids uponirradiation of light. They generate Brönsted or Lewis acids uponirradiation.

Use of triaryl sulfonium salts in additive fabrication applications isknown. Please see U.S. Pat. No. 6,368,769, to Asahi Denki Kogyo, whichdiscusses triaryl sulfonium salts with tetraryl borate anions, includingtetrakis(pentafluorophenyl)borate, and use of the compounds instereolithography applications. Triarylsulfonium salts are disclosed in,for example, J Photopolymer Science & Tech (2000), 13(1), 117-118 and JPoly Science, Part A (2008), 46(11), 3820-29. Triarylsulfonium saltsAr₃S⁺MX_(n) ⁻ with complex metal halide anions such as BF₄ ⁻, AsF₆ ⁻,PF₆ ⁻, and SbF₆ ⁻, are disclosed in J Polymr Sci, Part A (1996), 34(16),3231-3253.

The inventors have discovered that using an R-substituted aromaticthioether triaryl sulfonium tetrakis(pentafluorophenyl)borate cationicphotoinitiator as the cationic photoinitiator in a liquid radiationcurable resin for additive fabrication enables a liquid radiationcurable resin that attains a fast photospeed, attains goodthermal-stability, and attains good photo-stability.

In an embodiment, the R-substituted aromatic thioether triaryl sulfoniumtetrakis(pentafluorophenyl)borate cationic photoinitiator has atetrakis(pentafluorophenyl)borate anion and a cation of the followingformula (I):

wherein Y1, Y2, and Y3 are the same or different and wherein Y1, Y2, orY3 are R-substituted aromatic thioether with R being an acetyl orhalogen group.

In an embodiment, Y1, Y2, and Y3 are the same. In another embodiment, Y1and Y2 are the same, but Y3 is different. Y1, Y2, or Y3 are anR-substituted aromatic thioether with R being an acetyl or halogengroup. Preferably Y1, Y2, or Y3 are a para-R-substituted aromaticthioether with R being an acetyl or halogen group.

A particularly preferred R-substituted aromatic thioether triarylsulfonium tetrakis(pentafluorophenyl)borate cationic photoinitiator istris(4-(4-acetylphenyl)thiophenyl)sulfoniumtetrakis(pentafluorophenyl)borate.Tris(4-(4-acetylphenyl)thiophenyl)sulfoniumtetrakis(pentafluorophenyl)borate is known commercially as IRGACURE®PAG-290 (formerly known by the development code GSID4480-1) and isavailable from Ciba/BASF.

The inventors have also discovered that an R-substituted aromaticthioether triaryl sulfonium tetrakis(pentafluorophenyl)borate cationicphotoinitiator, for instance,tris(4-(4-acetylphenyl)thiophenyl)sulfoniumtetrakis(pentafluorophenyl)borate, is much more thermally-stable thanother cationic photoinitiators. The improved thermal-stability allowsliquid radiation curable resins for additive fabrication incorporating atriaryl sulfonium tetrakis(pentafluorophenyl)borate cationicphotoinitiator instead of other conventional cationic photoinitiators toretain their viscosity at elevated temperatures for long periods oftime.

Furthermore, the inventors have surprisingly found excellent performancein photo-stability of a liquid radiation curable resin for additivefabrication that comprises an R-substituted aromatic thioether triarylsulfonium tetrakis(pentafluorophenyl)borate cationic photoinitiator, forinstance tris(4-(4-acetylphenyl)thiophenyl)sulfoniumtetrakis(pentafluorophenyl)borate, in combination with high amounts ofinorganic filler, such as silica-based filler. The interaction withlight and inorganic filler, such as silica filler, creates addedstability problems in highly filled liquid radiation curable resins foradditive fabrication. However, use of R-substituted aromatic thioethertriaryl sulfonium tetrakis(pentafluorophenyl)borate cationicphotoinitiator in a liquid radiation curable resin enables the resin toattain comparable critical energy (Ec, E10) and depth of penetration(Dp) values to a resin incorporating a conventional cationicphotoinitiator while achieving much better photo-stability.

In accordance with embodiments of the invention, the liquid radiationcurable resin for additive fabrication includes a cationic polymerizablecomponent in addition to an R-substituted aromatic thioether triarylsulfonium tetrakis(pentafluorophenyl)borate cationic photoinitiator. Inother embodiments, the liquid radiation curable resins for additivefabrication include cationic polymerizable components, free-radicalphotoinitiators, and free-radical polymerizable components. In someembodiments, the liquid radiation curable resins for additivefabrication include an R-substituted aromatic thioether triarylsulfonium tetrakis(pentafluorophenyl)borate cationic photoinitiator andadditional cationic photoinitiators and/or photosensitizers, along witha cationic polymerizable component and, optionally, free-radicalpolymerizable components and free-radical photoinitiators.

The liquid radiation curable resin for additive fabrication of theinvention are curable by one or more LEDs operating at the appropriatewavelength. In an embodiment, the LEDs operate at a wavelength of from200 nm-460 nm, preferably from 300 nm-400 nm, more preferably from 340nm-375 nm.

The R-substituted aromatic thioether triaryl sulfoniumtetrakis(pentafluorophenyl)borate cationic photoinitiator can be presentin any suitable amount. In embodiments, up to 20 wt %, more preferablyup to 10 wt %, more preferably up to about 7 wt %. In embodiments, theR-substituted aromatic thioether triaryl sulfoniumtetrakis(pentafluorophenyl)borate cationic photoinitiator is present inan amount from about 0.1 wt % to about 20 wt %, preferably from about0.1 wt % to about 10 wt %, more preferably from about 0.1 wt % to about7 wt %, more preferably from about 0.2 wt % to about 4 wt %. In someembodiments, the R-substituted aromatic thioether triaryl sulfoniumtetrakis(pentafluorophenyl)borate cationic photoinitiator is present inan amount from 0.1 wt % to 2 wt %, preferably from 0.1 wt % to 1.5 wt %.

Other Cationic Photo initiators and Photosensitizers

In accordance with an embodiment, the liquid radiation curable resin foradditive fabrication includes a cationic photoinitiator in addition toan R-substituted aromatic thioether triaryl sulfoniumtetrakis(pentafluorophenyl)borate cationic photoinitiator. Any suitablecationic photoinitiator can be used, for example, those selected fromthe group consisting of onium salts, halonium salts, iodosyl salts,selenium salts, sulfonium salts, sulfoxonium salts, diazonium salts,metallocene salts, isoquinolinium salts, phosphonium salts, arsoniumsalts, tropylium salts, dialkylphenacylsulfonium salts, thiopyriliumsalts, diaryl iodonium salts, triaryl sulfonium salts, sulfoniumantimonate salts, ferrocenes, di(cyclopentadienyliron)arene saltcompounds, and pyridinium salts, and any combination thereof. Oniumsalts, e.g., iodonium salts, sulfonium salts and ferrocenes, have theadvantage that they are thermally-stable. Thus, any residualphotoinitiator does not continue to cure after the removal of theirradiating light. Cationic photoinitiators offer the advantage thatthey are not sensitive to oxygen present in the atmosphere.

Preferred mixtures of cationic photoinitiators include a mixture of:bis[4-diphenylsulfoniumphenyl]sulfide bishexafluoroantimonate;thiophenoxyphenylsulfonium hexafluoroantimonate (available as Chivacure1176 from Chitec); tris(4-(4-acetylphenyl)thiophenyl)sulfoniumtetrakis(pentafluorophenyl)borate (Irgacure PAG-290 or GSID4480-1 fromCiba/BASF), iodonium, [4-(1-methylethyl)phenyl](4-methylphenyl)-,tetrakis(pentafluorophenyl)borate (available as Rhodorsil 2074 fromRhodia),4-[4-(2-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfoniumhexafluoroantimonate (as SP-172) and SP-300 (both available from Adeka).

In some embodiments it is desirable for the liquid radiation curableresin for additive fabrication to include a photosensitizer. The term“photosensitizer” is used to refer to any substance that eitherincreases the rate of photoinitiated polymerization or shifts thewavelength at which polymerization occurs; see textbook by G. Odian,Principles of Polymerization, 3^(rd) Ed., 1991, page 222. Examples ofphotosensitizers include those selected from the group consisting ofmethanones, xanthenones, pyrenemethanols, anthracenes, pyrene, perylene,quinones, xanthones, thioxanthones, benzoyl esters, benzophenones, andany combination thereof. Particular examples of photosensitizers includethose selected from the group consisting of[4-[(4-methylphenyl)thio]phenyl]phenyl⁻methanone,isopropyl-9H-thioxanthen-9-one, 1-pyrenemethanol,9-(hydroxymethyl)anthracene, 9,10-diethoxyanthracene,9,10-dimethoxyanthracene, 9,10-dipropoxyanthracene,9,10-dibutyloxyanthracene, 9-anthracenemethanol acetate,2-ethyl-9,10-dimethoxyanthracene, 2-methyl-9,10-dimethoxyanthracene,2-t-butyl-9,10-dimethoxyanthracene, 2-ethyl-9,10-diethoxyanthracene and2-methyl-9,10-diethoxyanthracene, anthracene, anthraquinones,2-methylanthraquinone, 2-ethylanthraquinone, 2-tertbutylanthraquinone,1-chloroanthraquinone, 2-amylanthraquinone, thioxanthones and xanthones,isopropyl thioxanthone, 2-chlorothioxanthone, 2,4-diethylthioxanthone,1-chloro-4-propoxythioxanthone, methyl benzoyl formate, methyl-2-benzoylbenzoate, 4-benzoyl-4′-methyl diphenyl sulphide,4,4′-bis(diethylamino)benzophenone, and any combination thereof.

Additionally, photosensitizers are useful in combination withphotoinitiators in effecting cure with LED light sources emitting in thewavelength range of 300-475 nm. Examples of suitable photosensitizersinclude: anthraquinones, such as 2-methylanthraquinone,2-ethylanthraquinone, 2-tertbutylanthraquinone, 1-chloroanthraquinone,and 2-amylanthraquinone, thioxanthones and xanthones, such as isopropylthioxanthone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, and1-chloro-4-propoxythioxanthone, methyl benzoyl formate (Darocur MBF fromCiba), methyl-2-benzoyl benzoate (Chivacure OMB from Chitec),4-benzoyl-4′-methyl diphenyl sulphide (Chivacure'BMS from Chitec),4,4′-bis(diethylamino)benzophenone (Chivacure EMK from Chitec).

In an embodiment, the photosensitizer is a fluorone, e.g.,5,7-diiodo-3-butoxy-6-fluorone, 5,7-diiodo-3-hydroxy-6-fluorone,9-cyano-5,7-diiodo-3-hydroxy-6-fluorone, or a photosensitizer is

and any combination thereof.

The liquid radiation curable resin for additive fabrication can includeany suitable amount of the photosensitizer, for example, in certainembodiments, in an amount up to about 10% by weight of the composition,in certain embodiments, up to about 5% by weight of the composition, andin further embodiments from about 0.05% to about 2% by weight of thecomposition.

When photosensitizers are employed, other photoinitiators absorbing atshorter wavelengths can be used. Examples of such photoinitiatorsinclude: benzophenones, such as benzophenone, 4-methyl benzophenone,2,4,6-trimethyl benzophenone, and dimethoxybenzophenone, and1-hydroxyphenyl ketones, such as 1-hydroxycyclohexyl phenyl ketone,phenyl (1-hydroxyisopropyl)ketone,2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone, and4-isopropylphenyl(1-hydroxyisopropyl)ketone, benzil dimethyl ketal, andoligo-[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone] (EsacureKIP 150 from Lamberti). These photoinitiators when used in combinationwith a photosensitizer are suitable for use with LED light sourcesemitting at wavelengths from about 100 nm to about 300 nm.

A photosensitizer or co-initiator may be used to improve the activity ofthe cationic photoinitiator. It is for either increasing the rate ofphotoinitiated polymerization or shifting the wavelength at whichpolymerization occurs. The sensitizer used in combination with theabove-mentioned cationic photoinitiator is not particularly limited. Avariety of compounds can be used as photosensitizers, includingheterocyclic and fused-ring aromatic hydrocarbons, organic dyes, andaromatic ketones. Examples of sensitizers include compounds disclosed byJ. V. Crivello in Advances in Polymer Science, 62, 1 (1984), and by J.V. Crivello & K. Dietliker, “Photoinitiators for CationicPolymerization” in Chemistry & technology of UV & EB formulation forcoatings, inks & paints. Volume III, Photoinitiators for free radicaland cationic polymerization. by K. Dietliker; [Ed. by P. K. T. Oldring],SITA Technology Ltd, London, 1991. Specific examples includepolyaromatic hydrocarbons and their derivatives such as anthracene,pyrene, perylene and their derivatives, thioxanthones,α-hydroxyalkylphenones, 4-benzoyl-4′-methyldiphenyl sulfide, acridineorange, and benzoflavin.

The liquid radiation curable resin for additive fabrication can includeany suitable amount of the other cationic photoinitiator orphotosensitizer, for example, in certain embodiments, in an amount anamount from 0.1 to 10 wt % of the composition, in certain embodiments,from about 1 to about 8 wt % of the composition, and in furtherembodiments from about 2 to about 6 wt % of the composition. In anembodiment, the above ranges are particularly suitable for use withepoxy monomers.

In accordance with an embodiment, the liquid radiation curable resin foradditive fabrication includes a photoinitiating system that is aphotoinitiator having both cationic initiating function and free radicalinitiating function.

Cationically Polymerizable Component

In accordance with an embodiment, the liquid radiation curable resinsfor additive fabrication of the invention comprise at least onecationically polymerizable component, that is, a component whichundergoes polymerization initiated by cations or in the presence of acidgenerators. The cationically polymerizable components may be monomers,oligomers, and/or polymers, and may contain aliphatic, aromatic,cycloaliphatic, arylaliphatic, heterocyclic moiety(ies), and anycombination thereof. Suitable cyclic ether compounds can comprise cyclicether groups as side groups or groups that form part of an alicyclic orheterocyclic ring system.

The cationic polymerizable component is selected from the groupconsisting of cyclic ether compounds, cyclic acetal compounds, cyclicthioethers compounds, spiro-orthoester compounds, cyclic lactonecompounds, and vinyl ether compounds, and any combination thereof.

Examples of cationically polymerizable components include cyclic ethercompounds such as epoxy compounds and oxetanes, cyclic lactonecompounds, cyclic acetal compounds, cyclic thioether compounds, spiroorthoester compounds, and vinylether compounds. Specific examples ofcationically polymerizable components include bisphenol A diglycidylether, bisphenol F diglycidyl ether, bisphenol S diglycidyl ether,brominated bisphenol A diglycidyl ether, brominated bisphenol Fdiglycidyl ether, brominated bisphenol S diglycidyl ether, epoxy novolacresins, hydrogenated bisphenol A diglycidyl ether, hydrogenatedbisphenol F diglycidyl ether, hydrogenated bisphenol S diglycidyl ether,3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate,2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)-cyclohexane-1,4-dioxane,bis(3,4-epoxycyclohexylmethyl)adipate, vinylcyclohexene oxide,4-vinylepoxycyclohexane, vinylcyclohexene dioxide, limonene oxide,limonene dioxide, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate,3,4-epoxy-6-methylcyclohexyl-3′,4′-epoxy-6′-methylcyclohexanecarboxylate,ε-caprolactone-modified 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylates, trimethylcaprolactone-modified3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylates,β-methyl-δ-valerolactone-modified3,4-epoxycyclohexcylmethyl-3′,4′-epoxycyclohexane carboxylates,methylenebis(3,4-epoxycyclohexane), bicyclohexyl-3,3′-epoxide,bis(3,4-epoxycyclohexyl) with a linkage of —O—, —S—, —SO—, —SO₂—,—C(CH₃)₂—, —C(CBr₃)₂—, —C(CF₃)₂—, —C(CCl₃)₂—, or —CH(C₆H₅)—,dicyclopentadiene diepoxide, di(3,4-epoxycyclohexylmethyl)ether ofethylene glycol, ethylenebis(3,4-epoxycyclohexanecarboxylate),epoxyhexahydrodioctylphthalate, epoxyhexahydro-di-2-ethylhexylphthalate, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidylether, neopentylglycol diglycidyl ether, glycerol triglycidyl ether,trimethylolpropane triglycidyl ether, polyethylene glycol diglycidylether, polypropylene glycol diglycidyl ether, polyglycidyl ethers ofpolyether polyol obtained by the addition of one or more alkylene oxidesto aliphatic polyhydric alcohols such as ethylene glycol, propyleneglycol, and glycerol, diglycidyl esters of aliphatic long-chain dibasicacids, monoglycidyl ethers of aliphatic higher alcohols, monoglycidylethers of phenol, cresol, butyl phenol, or polyether alcohols obtainedby the addition of alkylene oxide to these compounds, glycidyl esters ofhigher fatty acids, epoxidated soybean oil, epoxybutylstearic acid,epoxyoctylstearic acid, epoxidated linseed oil, epoxidatedpolybutadiene, 1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene,3-ethyl-3-hydroxymethyloxetane,3-ethyl-3-(3-hydroxypropyl)oxymethyloxetane,3-ethyl-3-(4-hydroxybutyl)oxymethyloxetane,3-ethyl-3-(5-hydroxypentyl)oxymethyloxetane,3-ethyl-3-phenoxymethyloxetane, bis((1-ethyl(3-oxetanyl))methyl)ether,3-ethyl-3-((2-ethylhexyloxy)methyl)oxetane,3-ethyl-((triethoxysilylpropoxymethyl)oxetane,3-(meth)-allyloxymethyl-3-ethyloxetane,(3-ethyl-3-oxetanylmethoxy)methylbenzene,4-fluoro-[1-(3-ethyl-3-oxetanylmethoxy)methyl]benzene,4-methoxy-[1-(3-ethyl-3-oxetanylmethoxy)methyl]-benzene,[1-(3-ethyl-3-oxetanylmethoxy)ethyl]phenyl ether,isobutoxymethyl(3-ethyl-3-oxetanylmethyl)ether,2-ethylhexyl(3-ethyl-3-oxetanylmethyl)ether, ethyldiethyleneglycol(3-ethyl-3-oxetanylmethyl)ether, dicyclopentadiene(3-ethyl-3-oxetanylmethyl)ether,dicyclopentenyloxyethyl(3-ethyl-3-oxetanylmethyl)ether,dicyclopentenyl(3-ethyl-3-oxetanylmethyl)ether,tetrahydrofurfuyl(3-ethyl-3-oxetanylmethyl)ether,2-hydroxyethyl(3-ethyl-3-oxetanylmethyl)ether,2-hydroxypropyl(3-ethyl-3-oxetanylmethyl)ether, and any combinationthereof. Examples of polyfunctional materials that are cationicallypolymerizable include dendritic polymers such as dendrimers, lineardendritic polymers, dendrigraft polymers, hyperbranched polymers, starbranched polymers, and hypergraft polymers with epoxy or oxetanefunctional groups. The dendritic polymers may contain one type ofpolymerizable functional group or different types of polymerizablefunctional groups, for example, epoxy and oxetane functions.

In embodiments of the invention, the cationic polymerizable component isat least one selected from the group consisting of a cycloaliphaticepoxy and an oxetane. In a specific embodiment, the cationicpolymerizable component is an oxetane, for example, an oxetanecontaining 2 or more than 2 oxetane groups. In another specificembodiment, the cationic polymerizable component is a cycloaliphaticepoxy, for example, a cycloaliphatic epoxy with 2 or more than 2 epoxygroups.

In an embodiment, the epoxide is3,4-epoxycyclohexylmethyl-3′,4-epoxycyclohexanecarboxylate (available asCELLOXIDE™ 2021P from Daicel Chemical, or as CYRACURE™ UVR-6105 from DowChemical), hydrogenated bisphenol A-epichlorohydrin based epoxy resin(available as EPONEX™ 1510 from Hexion), 1,4-cyclohexanedimethanoldiglycidyl ether (available as HELOXY™ 107 from Hexion), a mixture ofdicyclohexyl diepoxide and nanosilica (available as NANOPDX™), and anycombination thereof.

The above-mentioned cationically polymerizable compounds can be usedsingly or in combination of two or more thereof.

The liquid radiation curable resin for additive fabrication can includeany suitable amount of the cationic polymerizable component, forexample, in certain embodiments, in an amount an amount up to about 80wt % of the composition, in certain embodiments, from about 10 to about80% by weight of the composition, and in further embodiments from about20 to about 70 wt % of the composition.

In accordance with an embodiment, the polymerizable component of theliquid radiation curable resin for additive fabrication is polymerizableby both free-radical polymerization and cationic polymerization. Anexample of such a polymerizable component is a vinyloxy compound, forexample, one selected from the group consisting ofbis(4-vinyloxybutyl)isophthalate, tris(4-vinyloxybutyl)trimellitate, andcombinations thereof. Other examples of such a polymerizable componentinclude those contain an acrylate and an epoxy group, or an acrylate andan oxetane group, on a same molecule.

In embodiments, the liquid radiation curable resin for additivefabrication of the present invention includes a photoinitiating system.The photoinitiating system can be a free-radical photoinitiator or acationic photoinitiator or a photoinitiator that contains bothfree-radical initiating function and cationic initiating function on thesame molecule. The photoinitiator is a compound that chemically changesdue to the action of light or the synergy between the action of lightand the electronic excitation of a sensitizing dye to produce at leastone of a radical, an acid, and a base.

Radical Photoinitiator

Typically, free radical photoinitiators are divided into those that formradicals by cleavage, known as “Norrish Type I” and those that formradicals by hydrogen abstraction, known as “Norrish type II”. TheNorrish type II photoinitiators require a hydrogen donor, which servesas the free radical source. As the initiation is based on a bimolecularreaction, the Norrrish type II photoinitiators are generally slower thanNorrish type I photoinitiators which are based on the unimolecularformation of radicals. On the other hand, Norrish type IIphotoinitiators possess better optical absorption properties in thenear-UV spectroscopic region. Photolysis of aromatic ketones, such asbenzophenone, thioxanthones, benzil, and quinones, in the presence ofhydrogen donors, such as alcohols, amines, or thiols leads to theformation of a radical produced from the carbonyl compound (ketyl-typeradical) and another radical derived from the hydrogen donor. Thephotopolymerization of vinyl monomers is usually initiated by theradicals produced from the hydrogen donor. The ketyl radicals areusually not reactive toward vinyl monomers because of the sterichindrance and the delocalization of an unpaired electron.

To successfully formulate a liquid radiation curable resin for additivefabrication, it is necessary to review the wavelength sensitivity of thephotoinitiator(s) present in the composition to determine if they willbe activated by the LED light chosen to provide the curing light.

In accordance with an embodiment, the liquid radiation curable resin foradditive fabrication includes at least one free radical photoinitiator,e.g., those selected from the group consisting of benzoylphosphineoxides, aryl ketones, benzophenones, hydroxylated ketones,1-hydroxyphenyl ketones, ketals, metallocenes, and any combinationthereof.

In an embodiment, the liquid radiation curable resin for additivefabrication includes at least one free-radical photoinitiator selectedfrom the group consisting of 2,4,6-trimethylbenzoyl diphenylphosphineoxide and 2,4,6-trimethylbenzoyl phenyl, ethoxy phosphine oxide,bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1,2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone,2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one,4-benzoyl-4′-methyl diphenyl sulphide,4,4′-bis(diethylamino)benzophenone, and4,4′-bis(N,N′-dimethylamino)benzophenone (Michler's ketone),benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone,dimethoxybenzophenone, 1-hydroxycyclohexyl phenyl ketone, phenyl(1-hydroxyisopropyl)ketone,2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone,4-isopropylphenyl(1-hydroxyisopropyl)ketone,oligo-[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone],camphorquinone, 4,4′-bis(diethylamino)benzophenone, benzil dimethylketal, bis(eta5-2-4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]titanium,and any combination thereof.

For LED light sources emitting in the 300-475 nm wavelength range,especially those emitting at 365 nm, 390 nm, or 395 nm, examples ofsuitable free-radical photoinitiators absorbing in this area include:benzoylphosphine oxides, such as, for example, 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Lucirin TPO from BASF) and2,4,6-trimethylbenzoyl phenyl, ethoxy phosphine oxide (Lucirin TPO-Lfrom BASF), bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide (Irgacure819 or BAPO from Ciba),2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1 (Irgacure 907from Ciba),2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone(Irgacure 369 from Ciba),2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one(Irgacure 379 from Ciba), 4-benzoyl-4′-methyl diphenyl sulphide(Chivacure BMS from Chitec), 4,4′-bis(diethylamino)benzophenone(Chivacure EMK from Chitec), and 4,4′-bis(N,N-dimethylamino)benzophenone(Michler's ketone). Also suitable are mixtures thereof.

Additionally, photosensitizers are useful in conjunction withphotoinitiators in effecting cure with LED light sources emitting inthis wavelength range. Examples of suitable photosensitizers include:anthraquinones, such as 2-methylanthraquinone, 2-ethylanthraquinone,2-tertbutylanthraquinone, 1-chloroanthraquinone, and2-amylanthraquinone, thioxanthones and xanthones, such as isopropylthioxanthone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, and1-chloro-4-propoxythioxanthone, methyl benzoyl formate (Darocur MBF fromCiba), methyl-2-benzoyl benzoate (Chivacure OMB from Chitec),4-benzoyl-4′-methyl diphenyl sulphide (Chivacure BMS from Chitec),4,4′-bis(diethylamino)benzophenone (Chivacure EMK from Chitec).

It is possible for LED UV light sources to be designed to emit light atshorter wavelengths. For LED light sources emitting at wavelengths frombetween about 100 and about 300 nm, it is desirable to employ aphotosensitizer with a photoinitiator. When photosensitizers, such asthose previously listed are present in the formulation, otherphotoinitiators absorbing at shorter wavelengths can be used. Examplesof such photoinitiators include: benzophenones, such as benzophenone,4-methyl benzophenone, 2,4,6-trimethyl benzophenone, anddimethoxybenzophenone, and, 1-hydroxyphenyl ketones, such as1-hydroxycyclohexyl phenyl ketone, phenyl (1-hydroxyisopropyl)ketone,2-hydroxy-1-[4-(2-hroxyethoxy)phenyl]-2-methyl-1-propanone, and4-isopropylphenyl(1-hydroxyisopropyl)ketone, benzil dimethyl ketal, andoligo-[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone] (EsacureKIP 150 from Lamberti).

LED light sources can also be designed to emit visible light. For LEDlight sources emitting light at wavelengths from about 475 nm to about900 nm, examples of suitable free radical photoinitiators include:camphorquinone, 4,4′-bis(diethylamino)benzophenone (Chivacure EMK fromChitec), 4,4′-bis(N,N′-dimethylamino)benzophenone (Michler's ketone),bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide (Irgacure 819 or BAPOfrom Ciba), metallocenes such as bis(eta5-2-4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]titanium(Irgacure 784 from Ciba), and the visible light photoinitiators fromSpectra Group Limited, Inc. such as H-Nu 470, H-Nu-535, H-Nu-635,H-Nu-Blue-640, and H-Nu-Blue-660.

In one embodiment of the instant claimed invention, the light emitted bythe LED is UVA radiation, which is radiation with a wavelength betweenabout 320 and about 400 nm. In one embodiment of the instant claimedinvention, the light emitted by the LED is UVB radiation, which isradiation with a wavelength between about 280 and about 320 nm. In oneembodiment of the instant claimed invention, the light emitted by theLED is UVC radiation, which is radiation with a wavelength between about100 and about 280 nm.

The liquid radiation curable resin for additive fabrication can includeany suitable amount of the free-radical photoinitiator, for example, incertain embodiments, in an amount up to about 10 wt % of thecomposition, in certain embodiments, from about 0.1 to about 10 wt % ofthe composition, and in further embodiments from about 1 to about 6 wt %of the composition.

Radically Polymerizable Component

In accordance with an embodiment of the invention, the liquid radiationcurable resin for additive fabrication of the invention comprises atleast one free-radical polymerizable component, that is, a componentwhich undergoes polymerization initiated by free radicals. Thefree-radical polymerizable components are monomers, oligomers, and/orpolymers; they are monofunctional or polyfunctional materials, i.e.,have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 100, or morefunctional groups that can polymerize by free radical initiation, maycontain aliphatic, aromatic, cycloaliphatic, arylaliphatic, heterocyclicmoiety(ies), or any combination thereof. Examples of polyfunctionalmaterials include dendritic polymers such as dendrimers, lineardendritic polymers, dendrigraft polymers, hyperbranched polymers, starbranched polymers, and hypergraft polymers; see US 2009/0093564 A1. Thedendritic polymers may contain one type of polymerizable functionalgroup or different types of polymerizable functional groups, forexample, acrylates and methacrylate functions.

Examples of free-radical polymerizable components include acrylates andmethacrylates such as isobornyl(meth)acrylate, bornyl(meth)acrylate,tricyclodecanyl(meth)acrylate, dicyclopentanyl(meth)acrylate,dicyclopentenyl(meth)acrylate, cyclohexyl(meth)acrylate,benzyl(meth)acrylate, 4-butylcyclohexyl(meth)acrylate, acryloylmorpholine, (meth)acrylic acid, 2-hydroxyethyl(meth)acrylate,2-hydroxypropyl(meth)acrylate, 2-hydroxybutyl(meth)acrylate,methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate,isopropyl(meth)acrylate, butyl(meth)acrylate, amyl(meth)acrylate,isobutyl(meth)acrylate, t-butyl(meth)acrylate, pentyl(meth)acrylate,caprolactone acrylate, isoamyl(meth)acrylate, hexyl(meth)acrylate,heptyl(meth)acrylate, octyl(meth)acrylate, isooctyl(meth)acrylate,2-ethylhexyl(meth)acrylate, nonyl(meth)acrylate, decyl(meth)acrylate,isodecyl(meth)acrylate, tridecyl(meth)acrylate, undecyl(meth)acrylate,lauryl(meth)acrylate, stearyl(meth)acrylate, isostearyl(meth)acrylate,tetrahydrofurfuryl(meth)acrylate, butoxyethyl(meth)acrylate,ethoxydiethylene glycol(meth)acrylate, benzyl(meth)acrylate,phenoxyethyl(meth)acrylate, polyethylene glycol mono(meth)acrylate,polypropylene glycol mono(meth)acrylate, methoxyethyleneglycol(meth)acrylate, ethoxyethyl(meth)acrylate, methoxypolyethyleneglycol(meth)acrylate, methoxypolypropylene glycol(meth)acrylate,diacetone(meth)acrylamide, beta-carboxyethyl(meth)acrylate, phthalicacid(meth)acrylate, dimethylaminoethyl(meth)acrylate,diethylaminoethyl(meth)acrylate, butylcarbamylethyl(meth)acrylate,n-isopropyl(meth)acrylamide fluorinated (meth)acrylate,7-amino-3,7-dimethyloctyl(meth)acrylate.

Examples of polyfunctional free-radical polymerizable components includethose with (meth)acryloyl groups such as trimethylolpropanetri(meth)acrylate, pentaerythritol(meth)acrylate, ethylene glycoldi(meth)acrylate, bisphenol A diglycidyl ether di(meth)acrylate,dicyclopentadiene dimethanol di(meth)acrylate,[2-[1,1-dimethyl-2-[(1-oxoallyl)oxy]ethyl]-5-ethyl-1,3-dioxan-5-yl]methylacrylate;3,9-bis(1,1-dimethyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro[5.5]undecanedi(meth)acrylate; dipentaerythritol monohydroxypenta(meth)acrylate,propoxylated trimethylolpropane tri(meth)acrylate, propoxylatedneopentyl glycol di(meth)acrylate, tetraethylene glycoldi(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,4-butanedioldi(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycoldi(meth)acrylate, polybutanediol di(meth)acrylate, tripropyleneglycoldi(meth)acrylate, glycerol tri(meth)acrylate, phosphoric acid mono- anddi(meth)acrylates, C₇-C₂₀ alkyl di(meth)acrylates,tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate,tris(2-hydroxyethyl)isocyanurate di(meth)acrylate, pentaerythritoltri(meth)acrylate, pentaerythritol tetra(meth)acrylate,dipentaerythritol hexa(meth)crylate, tricyclodecane diyl dimethyldi(meth)acrylate and alkoxylated versions (e.g., ethoxylated and/orpropoxylated) of any of the preceding monomers, and alsodi(meth)acrylate of a diol which is an ethylene oxide or propylene oxideadduct to bisphenol A, di(meth)acrylate of a diol which is an ethyleneoxide or propylene oxide adduct to hydrogenated bisphenol A,epoxy(meth)acrylate which is a (meth)acrylate adduct to bisphenol A ofdiglycidyl ether, diacrylate of polyoxyalkylated bisphenol A, andtriethylene glycol divinyl ether, and adducts of hydroxyethyl acrylate.

In accordance with an embodiment, the polyfunctional (meth)acrylates ofthe polyfunctional component may include all methacryloyl groups, allacryloyl groups, or any combination of methacryloyl and acryloyl groups.In an embodiment, the free-radical polymerizable component is selectedfrom the group consisting of bisphenol A diglycidyl etherdi(meth)acrylate, ethoxylated or propoxylated bisphenol A or bisphenol Fdi(meth)acrylate, dicyclopentadiene dimethanol di(meth)acrylate,[2-[1,1-dimethyl-2-[(1-oxoallyl)oxy]ethyl]-5-ethyl-1,3-dioxan-5-yl]methylacrylate, dipentaerythritol monohydroxypenta(meth)acrylate,dipentaerythritol hexa(meth)crylate, propoxylated trimethylolpropanetri(meth)acrylate, and propoxylated neopentyl glycol di(meth)acrylate,and any combination thereof.

In another embodiment, the free-radical polymerizable component isselected from the group consisting of bisphenol A diglycidyl etherdiacrylate, dicyclopentadiene dimethanol diacrylate,[2-[1,1-dimethyl-2-[(1-oxoallyl)oxy]ethyl]-5-ethyl-1,3-dioxan-5-yl]methylacrylate, dipentaerythritol monohydroxypentaacrylate, propoxylatedtrimethylolpropane triacrylate, and propoxylated neopentyl glycoldiacrylate, and any combination thereof.

In specific embodiments, the liquid radiation curable resins foradditive fabrication of the invention include one or more of bisphenol Adiglycidyl ether di(meth)acrylate, dicyclopentadiene dimethanoldi(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate,propoxylated trimethylolpropane tri(meth)acrylate, and/or propoxylatedneopentyl glycol di(meth)acrylate, and more specifically one or more ofbisphenol A diglycidyl ether diacrylate, dicyclopentadiene dimethanoldiacrylate, dipentaerythritol monohydroxypentaacrylate, propoxylatedtrimethylolpropane triacrylate, and/or propoxylated neopentyl glycoldiacrylate.

The liquid radiation curable resin for additive fabrication can includeany suitable amount of the free-radical polymerizable component, forexample, in certain embodiments, in an amount up to about 40 wt % of thecomposition, in certain embodiments, from about 2 to about 40 wt % ofthe composition, in other embodiments from about 10 to about 40 wt %,and in further embodiments from about 10 to about 25 wt % of thecomposition.

Stabilizers

In embodiments of the invention, the liquid radiation curable resins foradditive fabrication include a stabilizer. Stabilizers are often addedto the compositions in order to prevent a viscosity build-up, forinstance a viscosity build-up during usage in a solid imaging process.Useful stabilizers include those described in U.S. Pat. No. 5,665,792,the entire disclosure of which is hereby incorporated by reference. Suchstabilizers are usually hydrocarbon carboxylic acid salts of group IAand IIA metals. Most preferred examples of these salts are sodiumbicarbonate, potassium bicarbonate, and rubidium carbonate. Solidstabilizers are generally not preferred in filled compositions. A 15-23%sodium carbonate solution is preferred for formulations of thisinvention with recommended amounts varying between 0.05 to 3.0% byweight of composition, more preferably from 0.05 to 1.0 wt %, morepreferably from 0.1 to 0.5% by weight of composition. Alternativestabilizers include polyvinylpyrrolidones and polyacrylonitriles.

Other Components

Other possible additives include dyes, pigments, talc, glass powder,alumina, alumina hydrate, magnesium oxide, magnesium hydroxide, bariumsulfate, calcium sulfate, calcium carbonate, magnesium carbonate,silicate mineral, diatomaceous earth, silica sand, silica powder,titanium oxide, aluminum powder, bronze powder, zinc powder, copperpowder, lead powder, gold powder, silver dust, glass fiber, titanic acidpotassium whisker, carbon whisker, sapphire whisker, beryllia whisker,boron carbide whisker, silicon carbide whisker, silicon nitride whisker,glass beads, hollow glass beads, metaloxides and potassium titanatewhisker), antioxidants, wetting agents, photosensitizers for thefree-radical photoinitiator, chain transfer agents, leveling agents,defoamers, surfactants and the like.

In accordance with an embodiment, the liquid radiation curable resin foradditive fabrication can further include a chain transfer agent,particularly a chain transfer agent for a cationic monomer. The chaintransfer agent has a functional group containing active hydrogen.Examples of the active hydrogen-containing functional group include anamino group, an amide group, a hydroxyl group, a sulfo group, and athiol group. In an embodiment, the chain transfer agent terminates thepropagation of one type of polymerization, i.e., either cationicpolymerization or free-radical polymerization and initiates a differenttype of polymerization, i.e., either free-radical polymerization orcationic polymerization. In accordance with an embodiment, chaintransfer to a different monomer is a preferred mechanism. Inembodiments, chain transfer tends to produce branched molecules orcrosslinked molecules. Thus, chain transfer offers a way of controllingthe molecular weight distribution, crosslink density, thermalproperties, and/or mechanical properties of the cured resin composition.

Any suitable chain transfer agent can be employed. For example, thechain transfer agent for a cationic polymerizable component is ahydroxyl-containing compound, such as a compound containing 2 or morethan 2 hydroxyl-groups. In an embodiment, the chain transfer agent isselected from the group consisting of a polyether polyol, polyesterpolyol, polycarbonate polyol, ethoxylated or propoxylated aliphatic oraromatic compounds having hydroxyl groups, dendritic polyols,hyperbranched polyols. An example of a polyether polyol is a polyetherpolyol comprising an alkoxy ether group of the formula [(CH₂)_(n)O]_(m),wherein n can be 1 to 6 and m can be 1 to 100.

A particular example of a chain transfer agent is polytetrahydrofuransuch as TERATHANE™.

The liquid radiation curable resin for additive fabrication can includeany suitable amount of the chain transfer agent, for example, in certainembodiments, in an amount up to about 50% by weight of the composition,in certain embodiments, up to about 30% by weight of the composition,and in certain other embodiments from about 10% to about 20% by weightof the composition.

The liquid radiation curable resin for additive fabrication of theinvention can further include one or more additives selected from thegroup consisting of bubble breakers, antioxidants, surfactants, acidscavengers, pigments, dyes, thickneners, flame retardants, silanecoupling agents, ultraviolet absorbers, resin particles, core-shellparticle impact modifiers, soluble polymers and block polymers, organicfillers, inorganic fillers, or organic-inorganic hybrid fillers of sizesranging from about 8 nanometers to about 50 microns.

Inorganic Filler

In embodiments, an inorganic filler is present in an amount from 5 wt %to about 90 wt %, preferably from 10 wt % to 75 wt %, more preferablyfrom 30 to 75 wt %. The inorganic filler preferably comprises silica(SiO₂) nanoparticles or microparticles, or nanoparticles ormicroparticles that are substantially silica based, for instance,greater than 80 wt %, more preferably 90 wt %, more preferably 95 wt %of silica. Preferred silica nanoparticles are Nanopox products fromNanoresins, such as Nanopox A610. Suitable examples of such silicamicroparticles are NP-30 and NP-100 from AGC Chemicals, SUNSPACER™ 04.Xand 0.4×ST-3 from Suncolor Corporation. Examples of such silicananoparticles are SUNSPHERES™ 200 nm such as 0.2 and 0.2-STP-10. Pleasesee U.S. Pat. No. 6,013,714 for further examples of silica particles.However, depending on the size and other properties of the silicananoparticles or microparticles, the thermal-stability of the liquidradiation curable resin may decrease when certain silica nanoparticlesor microparticles are added to the liquid radiation curable resin due tothe acidity of the silica.

As mentioned above, the inventors have found a surprising combination ofa triaryl sulfonium tetrakis(pentafluorophenyl)borate cationicphotoinitiator, preferably, tris(4-(4-acetylphenyl)thiophenyl)sulfoniumtetrakis(pentafluorophenyl)borate, and high amounts of inorganic filler,preferably silica filler which comprises greater than 80 wt %, morepreferably 90 wt %, more preferably 95 wt % of silica. The combinationyields liquid radiation curable resins for additive fabrication thatattain excellent photo-stability and thermal-stability.

Nanoparticles are defined herein as particles having an average particlediameter in the range from 1 nm to 999 nm as measured using laserdiffraction particle size analysis in accordance with ISO13320:2009. Asuitable device for measuring the average particle diameter ofnanoparticles is the LB-550 machine, available from Horiba Instruments,Inc, which measures particle diameter by dynamic light scattering.Microparticles are defined herein as particles that have an averageparticle diameter in the range from 1 to about 100 microns as measuredin accordance with ISO13320:2009.

The second aspect of the instant claimed invention is a process offorming a three-dimensional object comprising the steps of forming andselectively curing a layer of a liquid radiation curable resin foradditive fabrication comprising a triaryl sulfoniumtetrakis(pentafluorophenyl)borate photoinitiator and repeating the stepsof forming and selectively curing a layer of a liquid radiation curableresin for additive fabrication comprising a triaryl sulfoniumtetrakis(pentafluorophenyl)borate photoinitiator a plurality of times toobtain a three-dimensional object. The process can be performed usingany suitable means of imaging radiation, such as an LED, a lamp, or alaser. Moreover, the process can be performed on a liquid radiationcurable resin contained in a vat or coated on a substrate. Preferably,the process is performed by one or more LEDs. The LEDs preferablyoperate from 200 nm-460 nm, preferably from 300 nm-400 nm, morepreferably from 340 nm-370 nm.

The third aspect of the instant claimed invention is a three-dimensionalobject formed from a liquid radiation curable resin for additivefabrication that comprises a triaryl sulfoniumtetrakis(pentafluorophenyl)borate cationic photoinitiator.

The fourth aspect of the instant claimed invention is a liquid radiationcurable resin for additive fabrication comprising 5 wt % to about 90 wt%, preferably from 10 wt % to 75 wt %, more preferably from 30 to 75 wt% of inorganic filler, said inorganic filler preferably comprisinggreater than 80 wt %, preferably greater than 90 wt %, more preferablygreater than 95 wt % of silica, that has a Dp of from about 4.5 mils toabout 7.0 mils, preferably from 4.5 mils to about 6.0 mils, morepreferably from 4.5 mils to about 5.5 mils, wherein the liquid radiationcurable resin for additive fabrication, when placed on a shaker tableset at 240 rpm and exposed to two 15 watt plant and aquarium lamps hung8 inches above the surface of the liquid radiation curable resin foradditive fabrication, has a gel time of greater than 200 hours,preferably greater than 250 hours.

The fifth aspect of the instant claimed invention is the use of anR-substituted aromatic thioether triaryl sulfoniumtetrakis(pentafluorophenyl)borate cationic photoinitiator with atetrakis(pentafluorophenyl)borate anion and a cation of the followingformula (I):

wherein Y1, Y2, and Y3 are the same or different and where Y1, Y2, or Y3are R-substituted aromatic thioether with R being an acetyl or halogengroup, on metal and metal alloys, such as alluminum alloy, steels,stainless steels, copper alloys, tin, or tin-plated steels.

The following examples further illustrate the invention but, of course,should not be construed as in any way limiting its scope.

EXAMPLES

These examples illustrate embodiments of the liquid radiation curableresins for additive fabrication of the instant invention. Table 1describes the various components of the liquid radiation curable resinsfor additive fabrication used in the present examples.

TABLE 1 Function in Component Formula Chemical Descriptor Supplier BYK A501 Bubble breaker Naphtha/methoxy propanol acetate BYK-Chemie NK EsterA-DOG Free radical [2-[1,1-dimethyl-2-[(1- Kowa polymerizableoxoallyl)oxy]ethyl]-5-ethyl-1,3-dioxan- compound 5-yl]methyl acrylate CD406 Free radical 1,4-Cyclohexanedimethanol diacrylate Sartomerpolymerizable compound Chivacure 1176 Cationic A mixture of: bis[4-Chitec Photoinitiator diphenylsulfoniumphenyl]sulfidebishexafluoroantimonate; thiophenoxyphenylsulfonium hexafluoroantimonateand propylene carbonate. Chivacure BMS Photosensitizing [4-[(4- Chitecagent methylphenyl)thio]phenyl]phenyl- methanone DG-0071 Stabilizer 22%of sodium carbonate solution Desotech DPHA Radical Dipentaerythritolhexaacrylate Sigma Polymerizable Aldrich Compound EPONOX 1510 CationicHydrogenated bisphenol A- Hexion Polymerizable epichlorohydrin basedepoxy resin Compound Heloxy 68 Cationic Neopentylglycol diglycidyletherHexion Polymerizable Compound HQMME Antioxidant Hydroquinone monomethylether Intermediate DG-0049 Pigment Pigment dispersion for color effectsDesotech dispersion Irgacure 184 Radical 1-Hydroxy-1-cyclohexyl phenylketone BASF Photoinitiator Irgacure PAG-290 Cationic tris(4-(4- BASFPhotoinitiator acetylphenyl)thiophenyl)sulfoniumtetrakis(pentafluorophenyl)borate Longnox 10 Antioxidant Pentaerythritoltetrakis[(3,5-di-tert- Longchem butyl-4-hydroxyphenyl)propionate] C&SInt. Nanopox A610 Filler in reactive 40% 15 nm of SiO₂ Particle in epoxyNanoresins monomer monomer OXT-101 Cationic 3-Ethyl-3-oxetanemethanolToagosei Polymerizable Compound Polyvinyl pyrrolidone AcidPoly[N-vinylpyrrolidinone]; PVP Sigma scavenger Aldrich Rhodorsil 2074Photoacid Iodonium, [4-(1-methylethyl)phenyl](4- Rhodia generatormethylphenyl)-, tetrakis(pentafluorophenyl)borate Rubidium carbonateAcid Dirubidium carbonate; Rb₂CO₃ Sigma scavenger Aldrich Silwet L 7600Leveling Polyalkyleneoxide modified Momentive agent polydimethylsiloxaneSR-399LV, J Radical Dipentaerythritol Sartomer Polymerizablemonohydroxypentaacrylate Compound SR-833S Radical TricyclodecaneDimethanol Diacrylate Sartomer Polymerizable Compound Sunspacer4.0X-ST-3 Filler SiO₂ Particle (4 micron average particle Suncolor size)TERATHANE 1000 Chain transfer Poly(tetramethylene ether) glycol Invistaagent for cationic monomers

Examples 1-7

Various liquid radiation curable resins for additive fabrication wereprepared using an R-substituted aromatic thioether triaryl sulfoniumtetrakis(pentafluorophenyl)borate cationic photoinitiator. A similarcomposition was prepared using an alternative antimony-free cationicphotoinitiator. These samples were tested according to the methods forworking curve measurement and dynamic mechanical analysis detailedbelow. Working curve data was obtained using a single UV LED “bare bulb”(Model No. NCSU033A; Nichia Corporation, Japan) having a peak wavelengthof 365 nm in a light curing apparatus, wherein the single LED light isbottom-mounted on a flat surface inside a 30° C. chamber and positionedin an upward-looking arrangement and pointing vertically according tothe below method. Real-time dynamic mechanical analysis was performedusing a mercury lamp with a 365 nm interference filter, respectively.The results are presented in Table 2 and Table 3.

Working Curve Measurement

The photo cure speed test using 365 nm LED light is used to measurevalues for Ec and Dp of the example and comparative example compositionsin Table 2 and Table 3. A single UV LED “bare bulb” (Model No. NCSU033A;Nichia Corporation, Japan) having a peak wavelength of 365 nm is used asthe LED light source in a light curing apparatus, wherein the single LEDlight is bottom-mounted on a flat surface inside a 30° C. chamber andpositioned in an upward-looking arrangement and pointing vertically. TheLED light is powered by a 3.30 V/0.050 A DC output from a ProgrammablePower Supply (Model No. PSS-3203; GW Instek).

A 10-mil sheet of polyester film (Melinex #515, Polybase Mylar D, 0.010gauge) is placed at a distance of 12 mm above from the bottom of the LEDlight bulb. A drop of the liquid resin is placed on the polyester filmover the center of the LED light. The resin is exposed to the LED lightthrough the polyester film for a specific time interval. The process isrepeated with fresh resin for 2, 4, 6, 8, 10 second exposure times or upto 12, 16, or 20 seconds for slow curing resin formulations.

After exposure to the LED light, the sample is allowed to age inside the30° C. chamber for at least 15 minutes, after which time any uncuredresin is removed from the exposed areas by blotting with a Kimwipe EX-L(Kimberly Clark). A thickness measurement is then taken on the center ofthe exposed area using an ABSOLUTE Digimatic Indicator (Model ID-C112CE,Mitutoyo Corporation, Japan). The measured thickness of each sample isplotted as a function of the natural logarithm of the exposure time. Thedepth of penetration (Dp; mil) of the resin composition is the slope ofthe least squares fit line. The Ec (sec) is the X-axis crossing point(Y=0) of the line. The E₃, E₄, or E₅ is, respectively, the time (inseconds) required to produce a layer having a thickness of 3, 4, or 5mils, respectively.

Alternatively, when the intensity of the incident light (mW/cm²) fromthe light source on the resin surface is known, the exposure energy(mJ/cm²) rather than the exposure time (in seconds) is used forcalculating the Dp and Ec values.

Measurement of Storage Shear Modulus (G) by Real Time Dynamic MechanicalAnalysis (RT-DMA)

Real Time Dynamic Mechanical Analysis (RT-DMA), including the storageshear modulus (G′), is carried out under ambient lab conditions (20-23°C. and 25-35% RH), on compositions undergoing curing using a StressTechRheometer (Reologicia Instruments AB, Sweden) with an 8 mm plate, a gapof 0.1 mm, and modified to include a mercury lamp light source (OMNICURESeries 2000 available from EXFO), fitted with a 365 nm interferencefilter (also available from EXFO) placed in the light path and aliquid-filled light guide for conveying light from the source to therheometer. The 365 nm interference filter produces the spectral outputshown in FIG. 1. The samples are evaluated under the followingparameters: 10 s of equilibrium time; frequency of 10 Hz; 50 mW/cm2light intensity by the IL 1400 radiometer with XRL140B detector(International Light, Newburyport, Mass.); 1.0 s exposure that starts at2.1 seconds from the beginning of data collection; FFT smoothing ofcurves; G′ taken at 2.5, 2.7, 3, 4, and 6 s from the beginning of datacollection by using the accompanying software for data analysis.

FIG. 2 shows a schematic of the RT-DMA apparatus. The liquid radiationcurable resin (1) is placed on a plane (2). The amount of liquid resinused should be approximately the amount indicated in the figure. Theplane is a quartz plate that is sold with the StressTech Rheometer. The8 mm plate (3) is positioned with a 0.1 mm gap (4) between the plate andthe plane. The gap is set via the software accompanying the StressTechRheometer. Light (5) is provided though the plane (2). Please see thepublication “Dynamic Mechanical Analysis of UV-Curable Coatings WhileCuring” by Robert W. Johnson available athttp://reologicainstruments.com/PDF%20files/BobJohnsonUVpaper.pdf, andhereby incorporated by reference in its entirety, for more informationon RT-DMA.

TABLE 2 Ex1 Ex2 Ex3 EBECRYL-3700 25 17.237 24.449 CD 406 7 6.846Celloxide 2021P 36 52.959 34.326 OXT-101 8.431 TERATHANE-1000 25 10.25424.449 Chivacure 1176 3.998 3.325 Irgacure PAG-290 4 2 2.2 Irgacure 1843 4.9 4.401 PVP 0.005 Rubidium carbonate 0.005 Silwet L 7600 0.196 BYK A501 0.02 Total 100 100 100 Dp (mil) 3.53 5.69 5.42 Ec (s) 1.13 1.15 1.22E3 (s) 2.64 1.96 2.13 E4 (s) 3.5 2.33 2.56 E5 (s) 4.65 2.78 3.08 G′ 0.4sec after light on (Pa) 1270 1150 3060 G′ 0.6 sec after light on (Pa)5510 10700 76900 G′ 0.9 sec after light on (Pa) 119000 99300 456000 G′1.9 sec after light on (Pa) 627000 277000 1580000 G′ 3.9 sec after lighton (Pa) 1030000 459000 2540000

TABLE 3 Ex4 Ex5 Ex6 Ex7 Comp1 Irgacure PAG 290 0.98 1.00 1.00 1.50Rhodorsil PI-2074 2.00 Chivacure BMS 1.00 Irgacure 184 6.00 6.00 6.006.00 6.00 SR399J 6.24 5.74 4.94 DPHA 7.02 4.00 NK Ester A-DOG 20.0020.00 15.57 15.57 15.57 Celloxide 2021P 45.84 45.84 Terathane1000 10.1913.19 OXT-101 9.17 9.17 15.70 15.70 15.70 Longnox 10 0.50 0.50 1.00 1.000.50 PVP 0.01 0.01 DG-0049 0.30 0.30 0.20 0.20 Epon 1510 54.30 54.3054.30 Total 100 100 100 100 100 G′ 0.5 sec after light on (Pa) 188109884 809 2140 449 G′ 0.7 sec after light on (Pa) 195100 123000 4492033620 21440 G′ 1.0 sec after light on (Pa) 742500 555100 360000 270900219400 G′ 2.0 sec after light on (Pa) 1726000 1400000 1099000 866900697800 G′ 4.0 sec after light on (Pa) 2305000 1968000 1565000 12610001014000

Examples 8-11

Various liquid radiation curable resins were prepared according tomethods well known in the art. The amount and type of the cationicphotoinitiator was varied from Chivacure 1176 (Comparative Examples 8,9, 10) to Irgacure PAG-290 (Examples 8, 9, 10, 11). Since Chivacure 1176is a 50/50 mixture of cationic photoinitiator and propylene carbonate,an amount of propylene carbonate was added to some of the formulationscontaining PAG-290 in order to keep the amount of cationicphotoinitiator plus propylene carbonate constant. Working curve data wasprepared using a solid state laser operating at a wavelength of 354.7 nmin accordance with the below method. Photo-stability data (hrs until geltime), and thermal-stability data (initial viscosity, 15 day viscosity,and 24 days viscosity) were measured in accordance with the belowmethods. The details of the compositions of each example (Ex) andcomparative example (Comp) are specified in Table 4 with each componentrepresented as weight percent of the total composition.

Working Curve Measurement

The working curve is a measure of the photospeed of the particularmaterial. It represents the relationship between the thickness of alayer of liquid radiation curable resin produced as a function of theexposure given. For all formulations, the exposure-working curve of theformula is determined using methods well known in the art.

The exposure response for each formulation is measured using a 20 gsample of the formulation in a 100 mm diameter petri dish held at 30° C.and 30% RH. The surface of the formulation is exposed with the indicatedlight source. The exposures are made in half-inch squares (exposureregions) which are scanned out by drawing consecutive parallel linesapproximately 25.4 microns apart on the surface of the liquid in thepetri dish at 72 mW. Different exposure regions are exposed to differentlevels of known incident energy to obtain different cured thicknesses.The spot diameter at the liquid surface is approximately 0.0277 cm indiameter. After waiting at least 15 minutes for the exposed panels toharden, the panels are removed from the petri dish and excess, uncuredresin is removed by blotting with a Kimwipe EX-L (Kimberly Clark). Filmthickness is measured with a Mitutoyo Model ID-C112CE IndicatorMicrometer. Film thickness is a linear function of the natural logarithmof the exposure energy; the slope of the regression is Dp (units ofmicron or mil) and Ec is the x-axis intercept of the regression fit(units of mJ/cm²). E10 is the energy required to cure a ten mil (254micron) layer.

Photo-Stability Measurement

45 g of each sample is added into 60 mL clear jars with a wide open top,available from FlackTek, Inc. The sample containing jars are placeduniformly across an Excella E5 platform shaker available from NewBrunswick Scientific Co., Inc. Each sample containing jar is securedwith clamps to the platform shaker. The light bank containing two 15watt plant & aquarium lamps (General Electric, F15T8 PL/AQ) is hung 8inches high over the shaker platform. The shaker speed is set to 240rpm. The samples are exposed right under the lamps and rotated dailyuntil the liquid sample is gelled. The liquid sample is gelled when asolid layer has formed on the surface of the liquid sample. The gel timeis collected to the nearest hour.

Thermal-Stability Measurement

After the liquid radiation curable resin is made, it is allowed to sitfor between 30 and 60 minutes or until it is degassed. Light tapping ofthe container holding the liquid radiation curable resin is performed toaccelerate the degassing process. The initial viscosity is then measuredusing a Rheometer from Paar Physica (Rheolab, MC10, Z3 cup and 1/50 sshear rate). The samples are held in the machine at the specified shearrate for 15 minutes before data is collected.

45 g of each sample is added into 60 mL clear jars with a wide open topavailable from FlackTek, Inc. The jar is capped loosely. The samplecontaining jars are placed in a 55° C. oven for a specified number ofdays. The samples containing jars are removed from the oven and allowedto cool to ambient conditions. The samples are then remixed and theviscosity is measured using the same equipment and technique mentionedabove.

The percentage change in viscosity is calculated by dividing theviscosity at a specified day by the initial viscosity. The result isthen multiplied by 100.

TABLE 4 Component Comp 8 Ex 8 Comp 9 Ex 9 Comp 10 Ex 10 Ex 11 NanopoxA610 33.62 33.62 34.61 34.78 33.57 33.57 34.72 Heloxy 68 5.71 5.71 5.885.91 5.70 5.70 5.89 OXT-101 3.81 3.81 3.92 3.94 3.80 3.80 3.93 SR-399LV3.42 3.42 3.52 3.54 3.42 3.42 3.54 SR-833S 2.29 2.29 2.36 2.37 2.29 2.292.39 Chivacure 1176 3.80 1.00 3.80 Irgacure PAG-290 1.90 0.50 1.90 0.50Propylene carbonate 1.90 1.90 Irgacure 184 0.40 0.40 0.40 0.40 0.40 0.400.40 Sunspacer 4.0X-ST-3 46.93 46.93 48.29 48.54 46.85 46.85 48.46 HQMME0.02 0.02 0.02 0.02 0.02 0.02 0.02 DG-0071 0.15 0.15 0.15 Total 100.00100.00 100.00 100.00 100.00 100.00 100.00 Total fillers 60.38 60.3862.13 62.45 60.28 60.28 62.35 Ec (mJ/cm2) 8.36 6.88 17.36 6.51 6.83 5.5112.45 Dp (mils) 4.90 1.73 14.82 3.92 4.38 1.37 5.12 E10 (mJ/cm2) 64.292209 34.09 83.41 66.78 8177 87.75 Photo-stability (hrs, gel time) 69 3979 55 199 199 No gel Initial Viscosity (cps, 30° C.) 1693 1655 2014 22271618 1468 2089 15 Day Viscosity (cps, 30° C.) 4249 2849 4084 3529 25492111 3120 15 Day Viscosity increase (%) 250.97 172.15 202.78 158.46157.54 143.80 149.35 24 Day Viscosity (cps, 30° C.) 6642 3312 5743 39172927 2297 3388 24 Day Viscosity increase (%) 392.32 200.12 285.15 175.89180.90 156.47 162.18 No gel = the sample did not gel after 300 hours.Comp = comparative example - not to be construed as an example of theinvention Ex = example of the invention

Discussion of Results

Improved reactivity of Examples 1-7 is demonstrated in comparison toComparative Example 1.

Comparative Example 8 uses a typical amount of a common cationicphotoinitiator used in many commercial liquid radiation curable resinsfor additive fabrication. Consequently, an E10 and Dp that is suitablefor an additive fabrication process is achieved.

Example 8 was designed to demonstrate the effects of a direct swap of anR-substituted aromatic thioether triaryl sulfoniumtetrakis(pentafluorophenyl)borate cationic photoinitiator for Chivacure1176. Example 8 shows a very low Dp and very high E10 due to theincreased absorbance of the R-substituted aromatic thioether triarylsulfonium tetrakis(pentafluorophenyl) borate cationic photoinitiatorover Chivacure 1176. The Dp is too low and the E10 far too high comparedto Comparative Example 8. Example 8 and Comparative Example 8 would thusnot perform similarly in an additive fabrication process. Consequently,the photo-stability of Example 8 is less than the photo-stability ofComparative Example 8. However, the thermal-stability of Example 8 isgreatly improved over the thermal-stability of Comparative Example 8.

Example 9 and Comparative Example 9 use a much lower amount of cationicphotoinitiator. Again, the Dp is significantly lower than in ComparativeExample 8. The reduced amount of cationic photoinitiators in Example 9and Comparative Example 9 yield additional improvement in thethermal-stability of the liquid radiation curable resin over Example 8and Comparative Example 8, respectively.

A stabilizer is added in Example 10, Example 11, and Comparative Example10. The stabilizer greatly improves the photo-stability of the liquidradiation curable resin for additive fabrication. Despite the very lowDp and high E10, Example 10 is able to achieve a photo-stability that issimilar to Comparative Example 10 which has a much more desirable Dp andE10. Example 11 demonstrates a Dp that is comparable to Example 8 and agreatly improved photo-stability over any other example or ComparativeExample. Example 10 and Example 11 also demonstrate improvedthermal-stability over Comparative Example 10.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one of ordinaryskill in the art that various changes and modifications can be madetherein without departing from the spirit and scope of the claimedinvention.

1. A liquid radiation curable resin for additive fabrication comprisingan R-substituted aromatic thioether triaryl sulfoniumtetrakis(pentafluorophenyl)borate cationic photoinitiator with atetrakis(pentafluorophenyl)borate anion and a cation of the followingformula (I):

wherein Y1, Y2, and Y3 are the same or different and wherein Y1, Y2, orY3 are R-substituted aromatic thioether with R being an acetyl orhalogen group.
 2. The liquid radiation curable resin for additivefabrication of claim 1 wherein the R-substituted aromatic thioethertriaryl sulfonium tetrakis(pentafluorophenyl)borate cationicphotoinitiator is present in an amount from about 0.1 wt % to about 20wt %, preferably from about 0.1 wt % to about 10 wt %, more preferablyfrom about 0.1 wt % to about 7 wt %, more preferably from about 0.2 wt %to about 4 wt % of the liquid radiation curable resin for additivefabrication.
 3. The liquid radiation curable resin for additivefabrication of claim 2 further comprising: a. from 2 to 40 wt % of aradically polymerizable compound b. from 10 to 80 wt % of a cationicallypolymerizable compound and c. from 0.1 to 10 wt % of a radicalphotoinitiator.
 4. The liquid radiation curable resin for additivefabrication of claim 1 wherein R is an acetyl group.
 5. The liquidradiation curable resin for additive fabrication of claim 1 wherein Y1,Y2, and Y3 are the same.
 6. The liquid radiation curable resin foradditive fabrication of claim 1 wherein the R-substituted aromaticthioether triaryl sulfonium tetrakis(pentafluorophenyl)borate cationicphotoinitiator is tris(4-(4-acetylphenyl)thiophenyl)sulfoniumtetrakis(pentafluorophenyl)borate.
 7. The liquid radiation curable resinfor additive fabrication of claim 1 wherein the R-substituted aromaticthioether triaryl sulfonium tetrakis(pentafluorophenyl)borate cationicphotoinitiator is present in an amount from 0.1 wt % to 2 wt %.
 8. Theliquid radiation curable resin for additive fabrication of claim 1further comprising a cationic photoinitiator that is not anR-substituted aromatic thioether triaryl sulfoniumtetrakis(pentafluorophenyl)borate cationic photoinitiator.
 9. The liquidradiation curable resin for additive fabrication of claim 1 furthercomprising a photosensitizer.
 10. The liquid radiation curable resin foradditive fabrication of claim 1 further comprising an inorganic filler,preferably present in an amount from about 5 wt % to about 90 wt %, morepreferably from about 10 wt % to about 75 wt %, more preferably fromabout 30 wt % to about 75 wt %.
 11. The liquid radiation curable resinfor additive fabrication of claim 10 wherein the inorganic filler issilica nanoparticles comprising at least 80 wt % silica, preferably 90wt % silica, more preferably 95 wt % silica.
 12. The liquid radiationcurable resin for additive fabrication of claim 1 further comprisingfrom about 0.1 to about 1 wt % of a stabilizer.
 13. The liquid radiationcurable resin of claim 12 wherein the stabilizer is a liquid Na₂CO₃solution.
 14. A liquid radiation curable resin for additive fabricationcomprising 5 wt % to about 90 wt %, preferably from 10 wt % to 75 wt %,more preferably from 30 to 75 wt % of inorganic filler, said inorganicfiller preferably comprising greater than 80 wt %, preferably greaterthan 90 wt %, more preferably greater than 95 wt % of silica, that has aDp of from about 4.5 mils to about 7.0 mils wherein the liquid radiationcurable resin for additive fabrication, when placed on a shaker tableset at 240 rpm and exposed to two 15 watt plant and aquarium lamps hung8 inches above the surface of the liquid radiation curable resin foradditive fabrication, has a gel time of greater than 200 hours,preferably greater than 250 hours.
 15. A process of forming athree-dimensional object comprising the steps of forming and selectivelycuring a layer of the liquid radiation curable resin composition foradditive fabrication of claim 1 with actinic radiation and repeating thesteps of forming and selectively curing a layer of the liquid radiationcurable resin composition for additive fabrication of claim 1 aplurality of times to obtain a three-dimensional object.
 16. The processof claim 15 wherein the source of actinic radiation is one or more LEDs.17. The process of claim 16 wherein the one or more LEDS emit light at awavelength of 200 nm-460 nm, preferably from 300 nm-400 nm, morepreferably from 340 nm to 370 nm, mire preferably having a peak at 365nm.
 18. A three-dimensional object formed from the liquid radiationcurable resin of claim
 1. 19. The use of an R-substituted aromaticthioether triaryl sulfonium tetrakis(pentafluorophenyl)borate cationicphotoinitiator with a tetrakis(pentafluorophenyl)borate anion and acation of the following formula (I):

wherein Y1, Y2, and Y3 are the same or different and where Y1, Y2, or Y3are R-substituted aromatic thioether with R being an acetyl or halogengroup, on metal and metal alloys, such as aluminum alloy, steels,stainless steels, copper alloys, tin, or tin-plated steels.